I have a prototype DAC board and was able to get it working with the current BSP kerenl, I can post some pictures later. A Volumio developer also has one and got the analog DAC working fine, but there was some trouble with SPDIF. At the moment I am a bit short of free time since so much (Pinebook, Rock64...) is happening at once, but if someone else wants to hack on this Tl Lim can probably provide one or two more DAC board samples....
Come have a chat in the Pine IRC channel >>